POLARIZATION OF THICK POLYVINYLIDENE FLUORIDE TRIFLUOROETHYLENE COPOLYMER FILMS/

Thick (800 mu m) polyvinylidene fluoride/trifluoroethylene (P(VDF-TrFE )) copolymer films for transducer applications are poled under applied voltage al elevated temperatures. By using different heat treatments, poling temperatures, and poling time, we are able to prepare a unifor mly poled film with a single resonance peak at 1.3 MHz, or a nonunifor mly poled film with two resonances (1.3 and 2.6 MHz), or a film with b imorph structure with a single resonance at 2.6 MHz. The nonuniform po larization which arises from charge injection from the cathode is chec ked by the pressure wave propagation method. The polarization mechanis ms in these thick films are expected to be similar to those previously reported for thin films. The result!, obtained in this work may lead to practical applications because they suggest a means for controlling transducer frequency by poling. (C) 1996 American Institute of Physic s.